Free-flowing, powdery composition containing alpha-liponic acid (derivates)

ABSTRACT

This free-flowing, powdery composition containing α-lipoic acid (derivatives) is distinguished by comprising, besides the lipoic acid component, from 0.1 to 25% by weight, based on the total weight of the composition, of a hydrophilic or hydrophobic silica-based flow aid which has a particle size (×100 value) of &lt;800 μm and a tamped density of from 50 to 600 g/l. The lipoic acid component is moreover not confined to the free acid form, but may also be at least partly in the form of its salts. Preferred flow aids are spray-dried precipitated silicas and/or highly dispersed silicas and/or amorphous silica gels. Besides the particle size and the tamped density, the flow aid employed may also be characterized by its specific surface area, which preferably ought to be between 30 and 1000 m 2 /g, or by the fact that the flow aid brings about a pH of between 3 and 11.5 in a concentration of 5% in aqueous solution. Also claimed is a process for producing this composition, in which the powdered lipoic acid component is mixed with the solid flow aid, and that particles of &gt;800 μm are removed from the solid mixture obtained in this way. This composition is used in solid dosage forms for pharmaceutical, dietetic or cosmetic applications and for producing solutions for infusions.

The present invention relates to a free-flowing, powdery compositioncontaining α-lipoic acid (derivatives), to a process for the productionthereof and to the use thereof.

α-Lipoic acid (thioctic acid, 1,2-dithiolane-3-pentanoic acid) has beenknown for about 50 years as a growth factor in microorganisms, but italso occurs as the R-(+) enantiomer in low concentrations in higherplants and animals. The physiological action of α-lipoic acid inhydrophilic and lipophilic media is as a coenzyme of the oxidativedecarboxylation of α-keto carboxylic acids (e.g. pyruvate,α-ketoglutarate). In addition, α-lipoic acid is also involved ascofactor in the degradation of certain amino acids. It moreovercontributes to the regeneration of vitamin C, vitamin E, glutathione andcoenzyme Q10. Further, α-lipoic acid and its relevant redox partnerdihydrolipoic acid have strongly antioxidant and occasionally alsoprooxidant properties; α-lipoic acid is therefore often referred to as“universal antioxidant”. Racemic α-lipoic acid is employed both as puresolid mixed with other components, in solid pharmaceutical formulations,but also in infusion solutions, as active pharmaceutical ingredient oras addition to food. Racemic α-lipoic acid is approved for the treatmentof liver disorders and neuropathies (e.g. diabetic polyneuropathy); itsuse as an efficient inhibitor of the replication of HIV-1 viruses hasbeen suggested (cf. Klin. Wochenschr. 1991, 69(15), 722-724). Injectionsolutions of α-lipoic acid are preferably employed chiefly in theinitial stage of corresponding clinical therapy. The R enantiomer ofα-lipoic acid has been in clinical phase II for applications in the areaof type II diabetes in Germany since December 2000 and in the USA sinceMay 2001.

Methods for synthesizing racemic α-lipoic acid and for enantiopure R- orS-α-lipoic acid are described or summarized for example in Crévisy etal., Eur. J. Org. Chem. 1998, 1949, Fadnavis et al., Tetrahedron Asym.1998, 9, 4109, Dhar et al., J. Org. Chem. 1992, 57, 1699, Adger et al.,J. Chem. Soc. Chem. Commun. 1995, 1563, Dasaradhi et al., J. Chem. Soc.Chem. Commun. 1990, 729, Gopalan et al., J. Chem. Soc. Perkin Trans. I1990, 1897, Yadav et al., J. Sci,. Ind. Res. 1990, 49, 400, Tolstikov etal., Bioorg. Khim. 1990, 16, 1670, Gopalan et al., Tetrahedron Lett.1989, 5705.

Compounds with a low solidification point, like the 60-62° C. of racemicα-lipoic acid or 47-50° C. of enantiopure R-(+)- or S-(−)-α-lipoic acid,form, at temperatures in the vicinity of their melting point, softsurfaces which result in adhesion of individual particles to oneanother. The sensitivity of racemic or enantiopure α-lipoic acid to theeffects of light and temperature, and a general tendency topolymerizability additionally have adverse effects. The reason for thissensitivity is that the characteristic disulfide bond in the strainedfive-membered ring in the lipophilic chain of the molecule can becleaved extremely easily. Such a cleavage is associated with anintermolecular formation of disulfide bridges, which leads to dimeric,oligmeric and polymeric lipoic acid derivatives (cf. DE 1617740). Thismay take place through the effect of light or temperature, but alsothrough the presence of nucleophiles (J. Org. Chem. 1969, 34, 3131).Oxidative decomposition is also disclosed in the literature (J. Org.Chem. 1975, 40, 58-62). This tendency to polymerization is even morepronounced for the pure enantiomers of α-lipoic acid than for theracemate. Because of the macroscopic properties of these lipoic acidpolymers, the product has a general tendency to form adhesions andlumps. Moreover, a higher content of these polymers means a greatertendency to lumps and a more pronounced reduction in the flowability ofthe product.

The usual method used for purifying crude α-lipoic acid isrecrystallization from organic solvents such as, for example, n-pentane,cyclohexane, methylcyclohexane, ethyl acetate, or mixtures of solvents(e.g. of ethyl acetate and hexane), as described for example in Brookeset al., J. Chem. Soc. Perkin Trans. 1 1988, 9, Segre et al., J. Am.Chem. Soc. 1957, 3503, Walton et al., J. Am. Chem. Soc. 1955, 77, 5144,Acker et al., J. Am. Chem. Soc. 1954, 76, 6483.

Also implemented industrially are processes for the extraction and/orcrystallization of α-lipoic acid, which provide for the use of organicsolvents having a dielectric constant ∈ of from 2.5 to 5.5 (DE 42 35912) or 1.95 to 2.4 (EP 1 100 793).

Working up the mother liquors to increase the yield and thus theefficiency of the process is technically very complicated and generallyleads to a deterioration in the flowability and to an increase in thetendency to lumps. DE 197 26 519 A1 proposes, as alternative additionalmethod for purifying lipoic acid which has previously beenrecrystallized from a mixture of cyclohexane and ethyl acetate, atreatment of the crude material enriched with lipoic acid with liquid orsupercritical carbon dioxide. According to DE 199 38 621, dissolvingcrude α-lipoic acid in dilute aqueous alkaline solution, removal ofsolid impurities present by filtration and reacidification results in acrystalline α-lipoic acid which is distinguished by the absence ofimpurities such as 1,2,3-trithiane-4-valeric acid (epilipoic acid) andthe absence of organic solvents.

EP-A 733 363 describes an agglomerated granulate of α-lipoic acid whichis obtained by means of an elaborate process after introducing α-lipoicacid into a fluidized bed device by spraying an α-lipoic acid solutiononto the introduced material while simultaneously removing the solvent.Such an α-lipoic acid has a specific surface area of >0.7 m²/g and aproportion of mesopores with a diameter between 2 and 30 nm. This highspecific surface area leads, in conjunction with different particlesizes, frequently to demixing, with the larger particles moving fasterthan the small ones, especially during transport, during transfer orconveying. The shape of the particles of this agglomerated granulatealso impairs the flowability of the product, because an irregularsurface leads to increased friction and to more ensnarement of theparticles by one another. In addition, the residual solvent content insuch agglomerated granulate results in increased particle adhesion inthe product which is mediated by capillary fluids in the partly orcompletely filled mesopore space.

The processes known in the prior art make it possible, despite aconsiderable increase in technical complexity and with yields which areunfavorable for commercial production of α-lipoic acid, for theflowability of the product to be improved to only a very limited extentand moreover insufficiently for many industrial applications. Theα-lipoic acid qualities obtainable to date are thus in a form which isunfavorable even just for further processing to solid dosage forms. Itis also a well-known fact that in the production of solid dosage formsof α-lipoic acid even apparently well-tried formulas sometimes giveinexplicable results with α-lipoic acid batches differing in provenance,even if all the process procedures are complied with, usually beingmanifested by insufficient qualities of product. In addition, althoughit is certainly acknowledged that, for example, the particle sizedistribution of the α-lipoic acid batch employed represents an importantcharacteristic for tabletability, it has not yet been possible tospecify the key parameters appropriately. If not all the importantbinding mechanisms (sintered bridges, crystallization and structuralmodifications, liquid bridges, chemical bonds, adhesion throughcapillary fluids) are known, it is usually impossible to preventparticle agglomerations.

The addition of various types of flow aids is widespread inpharmaceutical technology for active ingredients of solid dosage formsin order to reduce the adhesive forces between particles which arecaused by particle adhesion, electrostatic adhesion, van der Waalsforces or liquid bridges. Examples of such flow aids in the form ofsynthetic silicas which are suitable for preventing sintering processesare Aerosil® 200 or Aerosil® 380 (both synthetic, highly dispersedsilicas produced by the high-temperature hydrolysis process by DegussaAG) (Pharm. Ind. 1970, 32, 478). However, it was not possible to predictwhether use of flow aids in combination with α-lipoic acid leads toimproved qualities of product, or which specifications suitable flowaids ought to have.

The object of the present invention was thus to provide a compositioncontaining α-lipoic acid (derivatives) which if possible shows notendencies to agglomeration and which is not prone to clumping andadhere either. In addition, it was intended that the composition beprocessed further easily and without great efforts to solid dosage formsfor pharmaceutical, dietetic or cosmetic purposes.

This object has been achieved with the aid of a free-flowing, powderycomposition which comprises a lipoic acid component and from 0.1 to 25%by weight, based on the total weight of the composition, of asilica-based flow aid which has a particle size (×100 value) of <800 μmand a tamped density of from 50 to 600 g/l.

In this connection, the “×100 value” means, in contrast to the d50value, that 100% of the particles employed have maximally the sizestated in each case.

The claimed composition has distinctly improved properties in terms offlowability, flow behavior, sintering tendency and piling stability andits handling as solid during transfer or conveying is facilitated. Thiswas not thus to be expected.

The composition is particularly distinguished by a markedly improvedflowability compared with prior art qualities and additionally by asignificantly improved flow behavior. This is because, surprisingly, theso-called “core flow” is almost completely suppressed in the compositionof the invention through the use of specific flow aids in contrast toother flow aids. Thus, virtually the whole amount of powder moves duringtransfer, pouring or emptying, and the unwanted formation of “deadzones” is nearly completely suppressed.

Racemic α-lipoic acid and dihydrolipoic acid, enantiopure R-(+)- orS-(−)-α-lipoic acid and -dihydrolipoic acid or any mixtures thereof areto be regarded as preferred lipoic acid components. In addition,α-lipoic acid or else its natural lipoic acid redox partnerdihydrolipoic acid may be wholly or partly in the form of their salts.Suitable salts in this connection are, in particular, the sodium,potassium, ammonium, magnesium or creatine lipoate and/or the sodium,potassium, magnesium or creatine dihydrolipoate. It is additionallypossible for the lipoic acid and/or dihydrolipoic acid to be wholly orpartly in the form of a salt with basic amino acids such as, forexample, lysine, arginine or ornithine.

As described, it was possible to achieve the object on which thisinvention is based through the addition of certain flow aids to α-lipoicacid. Flow aids which have proved to be particularly suitable in thisconnection for achieving the desired improvements in quality andhandling of α-lipoic acid are hydrophilic spray-dried precipitatedsilicas such as, for example, Sipernat® 22 S, Sipernat® 50 S andSipernat® 500 LS (Degussa AG), or hydrophilic highly dispersed silicassuch as, for example, of the Aerosil® 200 type, and hydrophobic silicassuch as, for example, of the Aerosil® R972 type. The hydrophilicprecipitated silicas of the Sipernat® 22 S, Sipernat® 50 S and Sipernat®500 LS type moreover comply with the requirements for the food additiveE 551 of the EU directive 2000/63/EU and are thus authorized for examplefor use in dry food products in powder form (including types of sugar)up to a maximum quantity of 10 g/kg and for powdered flavorings up to amaximum quantity of 1000 mg/kg. Flow aids which have likewise provedsuitable for the purposes of the present invention are amorphous silicagels like those represented for example by the Sylox 2, 15 & T450 type(GRACE Davison, Columbia).

The proportion of flow aid component in the composition of the inventionshould be between 0.1 and 25% by weight based on the total weight of theproduct of the invention. Preferred proportions by weight of the flowaid are to be regarded as ranges between 1.0 and 10.0% by weight andparticularly preferably those between 1.5 and 5.0% by weight. Ranges of2.0-3.0% by weight are most preferred. All the proportions by weightstated here in relation to the flow aid are based on racemic oroptically pure α-lipoic acid. This means that on use of lipoic acidderivatives or salts the stated dosage quantities correspond to thosefor free lipoic acid, for which reason they must be adjusted for thechanged molecular weight.

The proportion of active ingredient component in the composition of theinvention is preferably 50-99.9% by weight. A proportion of activeingredient component of 75-99.0% by weight is particularly preferred,and a proportion of 90.0-98.0% by weight is most preferred.

The hydrophilic or hydrophobic flow aids normally have excellentintrinsic flowability and can be adjusted by grinding specifically inrelation to their features, essential to the invention, of particle sizeand tamped density.

In this connection, particle sizes (×100 value) which have proved to beparticularly suitable in relation to the flow aid are <600 μm and inparticular between 50 and 400 μm. Preferred ranges which have emerged inrelation to the tamped density parameter are from 75 to 100 g/l, and itshould be noted that these data relate to non-sieved flow aids.

For particular applications the specific surface area of the flow aidmay also be important, which is why the present invention regards rangesbetween 30 and 1000 m²/g and in particular those between 190 and 450m²/g as preferred. The specific surface areas were in this connectiondetermined with an Areameter using nitrogen.

The pH which the flow aids employed in each case attain in aqueoussolution may likewise be important. In this connection, the presentinvention has preference for flow aids which yield a pH of from 3.0 to11.5 and in particular of from 6.0 to 7.0 in a concentration of 5% inaqueous solution.

A further advantage of the composition of the invention is to beregarded as being the fact that the lipoic acid component employed maybe of any origin, i.e. the flowability is improved regardless of thesynthesis route used for the preparation. The solvent and polymercontent of the lipoic acid component is also immaterial within the scopeof the usual specifications. Also suitable for the composition of thepresent invention are solvent-free α-lipoic acids like those describedin DE 199 38 621 A, or prepared as described in DE 197 26 519 A1, DE 4235 912 A, DE 198 34 608 A1, EP 586 987, DE 198 45 517 A1, EP 733 363 orEP 593 896, or purified racemic or enantiopure α-lipoic acids.

Besides the described composition, the present invention also claims aprocess for the production thereof, in which

-   (a) the powdered lipoic acid component is mixed with the solid flow    aid, and then-   (b) particles of >800 μm are removed from the resulting solid    mixture.

It is moreover possible for the purposes of the present invention torepeat process steps (a) and/or (b) as often as desired.

The lack of complexity and the directness of the present process alsorepresent considerable advantages of the present invention. Smalleramounts of the composition of the invention can be produced in a simplemanner by mixing in a Turbula mixer for 3 minutes and then sieving. Forindustrial batches, mixing implements with low shear forces are to bepreferred in process step (a), as are represented by free-fall mixers inthe form of drum, V and tumbler mixers, horizontally operating paddleand plowshare mixers (e.g. Lödige mixers), vertically operating conicalmixers, especially with flat-cut screws of the Nauta type, or Eirichmixers with diagonal mixing implements; also suitable are mixers withrapidly rotating mixing implements, mixers with pulsating air and screwor double screw mixers. Short mixing times of from 5 to 30 min durationand in particular 10 to 15 minutes, and maximally fine distribution ofthe α-lipoic acid may overall be advantageous. It may therefore also beadvisable to introduce the lipoic acid component by spraying a solutionof the lipoic acid component onto a carrier silica with simultaneousremoval of the solvent. Alternatively, metering in of the flow aid in aspray tower is also a particularly preferred embodiment of the presentinvention.

This is because moreover the sequence of addition of the flow aid and ofthe lipoic acid component is immaterial for the present process.However, the present invention preferably provides for addition inprocess stage (a) of at least one of the two components in portions.However, the components can be overall added in any frequency andproportions and at any speed.

It is thus possible with the aid of a simple process to mix the lipoicacid component rapidly and efficiently with the hydrophilic orhydrophobic flow aid component with exposure to low shear forces.

A lipoic acid-containing composition produced in this way inter alia caneasily be processed further to appropriate dosage forms, for which thepresent invention provides the use in solid dosage forms forpharmaceutical, dietetic and/or cosmetic applications. It is possible inparticular to produce, in a simplified manner, compressed administrationforms and particularly preferably tablets with a high active ingredientcontent for oral applications, as are employed for example within theframework of a clinical therapy of diabetic polyneuropathy or type 2diabetes.

In addition, the invention also includes the use of the composition forproducing solutions for infusion.

Compared with lipoic acid-containing compositions disclosed to date inthe prior art, the composition of the invention displays generallyimproved properties in relation to flowability, flow behavior, sinteringtendency and piling stability. In addition, the handling as solid duringtransfer, pouring and/or conveying is significantly facilitated, whichis why the present invention represents a considerable improvement ofthe lipoic-containing compositions disclosed to date.

These advantages of the free-flowing, powdery composition containingα-lipoic acid (derivatives) are to be illustrated by the followingexamples.

EXAMPLES

The following methods were employed to assess the properties of theproduct.

(a) Flowability Through Orifice Apparatuses.

The flowability without pressure treatment was determined by usingsiliconized glass orifice vessels with different orifice diameters(Seifen, Öle, Fette, Wachse 1968, 94, 12). The assessment took place inaccordance with (rating) scores: 1=very good flow behavior (the powderto be investigated flows continuously out of orifice apparatus No. 1with the smallest orifice) to score 6=inadequate flow behavior (thepowder does not even flow out of measurement vessel No. 5 with thelargest orifice). The measurement method was carried out always with thesame sequence of orifice vessels 1 to 6. The measurement vessel withwhich the powdery composition just flows continuously out was determined(table 1). TABLE 1 Assessment of the flowability with glass orificevessels Assessment when the powder Orifice width flows through justVessel No. Ø [mm] continuously 1 2.5 very good 2 5 good 3 8 quite good 412 just adequate 5 18 deficient 6 inadequate (powder does not flowthrough No. 5)(h = 80 mm, Ø (internal) = 38 mm)

(b) Flowability Through Height of Conical Heap

A metal sieve was fastened at a distance of 30-100 mm above a solidmetal cylinder with a diameter of 50 mm and a height of about 80 mm. Thedistance between metal sieve and metal cylinder depended on theflowability of the powder to be measured and was somewhat larger thanthe height of the conical heap of the powder with the worst flow in theparticular test series. The sieve was fixed at this height, and thepowder was poured onto the sieve and slowly passed through it manuallywith the aid of a spatula. The descending powder thus forms a conicalheap on the metal cylinder. The powder was then passed through the sieveuntil a cone with geometrically regular shape had formed on thecylinder. The sieve was then removed, and the height of the conical heapwas measured. The angle of repose of the tested powder can be determinedfrom the height of the conical heap and the diameter of the metalcylinder. Since the diameter of the cone is constant, the height of theconical heap can also be used as direct measure of the flowability.Powders of very good flowability have a height of 15-20 mm for theconical heap; powders with a height of >50 mm for the conical heap havea poor flow behavior (table 2). TABLE 2 Assessment of the flowabilitywith height of the conical heap Height of conical heap [mm] AssessmentScore <20 very good 1 21-30 good 2 31-40 just adequate 3 41-50 deficient4 >50 inadequate 5

(c) Pressure Resistance

Powdered products tend to cake together on piling in sacks, drums orhoppers. The following test is used to assess their “piling stability”:a steel cylinder with an internal diameter of 50 mm is filled to aheight of about 20 mm with the powder to be tested, which is loaded witha plunger weighing 1.2 kg and with a defined additional weight. Theduration of the exposure to pressure can be chosen appropriate for theparticular stress on the powder during packaging, transport and storage.The additional weight used in this test design amounted to about0.16-0.17 kg/cm², corresponding to the weight of 10 to 12 sacks of agiven size, each with a filled weight of 50 kg, lying one on top of theother. After exposure to pressure for 24 hours, the additional weightwas removed, the two cylinders were carefully rotated by 180° by hand,and the powder tablet was expelled from the casing with the aid of theplunger. The hardness of the powder tablet is regarded as a measure ofthe pressure resistance; it can be measured subjectively or with the aidof a drum sieve: for the measurement, the powder tablet was placed in acylindrical drum sieve. The drum sieve was rotated at 60 rpm with theaid of a motor, and the time after which the tablet had only half theweight was determined. For this purpose, a balance which displayed theabraded powder weight was located underneath the sieve. TABLE 3 Visualassessment of the pressure resistance Score Behavior characteristics 1 =very good completely unchanged and flowing smoothly through orificevessel No. 2 (table 1) 2 = good partly loosely adherent, easilydisintegrating into the original state 3 = quite good loosely shaped;very substantially disintegrating to powder under gentle finger pressure4 = adequate loosely caked; still disintegrating very finely with fingertest 5 = deficient semisolid caking; no longer disintegrating veryfinely with finger test 6 = inadequate solidly shaped

Test Results

Comparative examples 1 to 2 were carried out with compositionsexclusively containing lipoic acid produced according to the prior art.(Example 1: according to EP 593 896; example 2: according to DE 199 38621 A1)

Comparative examples 3 to 5 were carried out with compositions whichcontain lipoic acid produced according to the prior art of example 2 andnon-inventive flow aids.

Examples 6 to 19 of the invention were carried out with compositions ofthe invention which contained lipoic acid produced according to example2 and flow aids of the invention.

All lipoic acid compositions combined with flow aid were produced bymixing in a Turbula mixer for 3 minutes, followed by sieving through a600 μm sieve.

The results in terms of the flow score are always considerably better inexamples 6-19 than in example 2 (control).

Comparative example 5 serves as control for the height of the conicalheap. The results in terms of this are likewise all better in examples6-17.

The pressure resistance increases as a function of the concentration inthe examples of the invention. With lipoic acid contents of 3.0% byweight, the increase in the scores is at least 1.5 in relation toexample 2 (example 19: scores of 2.5 with 2.0% by weight). TABLE 4Results Height of Proportion Flow conical heap Pressure # Flow aid byweight score [mm] resistance 1 n/a n/a 4 30 4-5 2 n/a n/a 6 notmeasurable, 6 cone breaks off 3 Sipernat  ® 1.0 5 not measurable, 5-6 4320 1.5 5 cone breaks off 5-6 5 2.0 4 29 5 6 Sipernat  ® 1.0 2 25 6 722S 1.5 2 22 5-6 8 2.0 2 21 5 9 3.0 2 20 4-5 10 Sipernat ® 1.0 2 23 5 1150S 1.5 2 21 4-5 12 2.0 2 19 4 13 3.0 2 19 4 14 Sipernat ® 1.0 2 22 4-515 500LS 1.5 2 19 4 16 2.0 2 19 3-4 17 3.0 2 20 3-  18 Silox ™ 2 1.5 4n/a 4-5 19 2.0 3 n/a 3-4“n/a”: not ascertainable

1-16. (canceled)
 17. A composition comprising a lipoic acid componentand from 0.1 to 25% by weight, based on the total weight of thecomposition, of a silica-based flow aid which has a particle size (×100value) of <800 μm and a tamped density of from 50 to 600 g/l, whereinthe composition is free-flowing and powdery.
 18. The composition asclaimed in claim 17, wherein the lipoic acid component is racemicα-lipoic acid, dihydrolipoic acid, enantiopure R-(+)- or S-(−)-α-lipoicacid, enantiopure R-(+)- or S-(−)-α-dihydrolipoic acid or mixturesthereof.
 19. The composition as claimed in claim 17, wherein at least aportion of the lipoic acid component is a salt.
 20. The composition asclaimed in claim 17, wherein the flow aid is present in an amount offrom 1.0 to 10.0% by weight based on the total weight of thecomposition.
 21. The composition as claimed in claim 17, wherein theflow aid is a hydrophilic spray-dried precipitated silica, a hydrophilichighly dispersed silica or a hydrophobic silica.
 22. The composition asclaimed in claim 17, wherein the flow aid is an amorphous silica gel.23. The composition as claimed in claim 17, wherein the flow aid has aparticle size (×100 value) of <600 μm.
 24. The composition as claimed inclaim 17, wherein the flow aid has a tamped density of from 75 to 100g/l.
 25. The composition as claimed in claim 17, wherein the flow aidhas a specific surface area of from 30 to 1000 m²/g.
 26. The compositionas claimed in claim 17, wherein the flow aid brings about a pH of from3.0 to 11.5 in a concentration of 5% in aqueous solution.
 27. A processfor producing a composition as claimed in claim 17, wherein (a) thepowdered lipoic acid component is mixed with the solid flow aid, and (b)particles of >800 μm are removed from the resulting solid mixture. 28.The process as claimed in claim 17, wherein a free-fall mixer, drummixture, a V mixer, a tumbler mixer, a horizontally operating paddlemixer, a plowshare mixer a Lödige mixer, a vertically operating conicalmixer, or a Eirich mixer with diagonal mixing implements are employedfor process stage (a).
 29. The process as claimed in claim 27, whereinat least one of the lipoic acid component or flow aid is added inportions to the mixing procedure in process stage (a).
 30. A soliddosage form comprising the composition of claim 17 and a pharmaceuticaladjuvant.
 31. A solid dosage form as claimed in claim 14, in acompressed form.
 32. A solution for infusion comprising the compositionof claim 17 in a solution.
 33. The composition of claim 17, wherein thesalt is a sodium, potassium, ammonium, magnesium, or creatine lipoate.34. The composition of claim 17, wherein the salt is a sodium,potassium, magnesium or creatine dihydrolipoate.
 35. The composition ofclaim 17, wherein said salt is a salt of a basic amino acid.
 36. Thecomposition of claim 35, wherein said basic amino acid is lysine,arginine or ornithine.
 37. The composition of claim 20, wherein saidproportion is from 1.5 to 5.0%.
 38. The composition of claim 23, whereinsaid particle size (×100 value) is between 50 and 400 microns.
 39. Thecomposition as claimed in claim 25, wherein the specific surface area isfrom 190 to 450 m²/g.
 40. The composition of claim 26, wherein the flowaid brings about a pH of from 6.0 to 7.0 in a concentration of 5% inaqueous solution.
 41. The process of claim 27, wherein the verticallyoperating conical mixer has flat cut screws of the Nauta type.